An acoustic imaging transducer typically consists of an array of piezoelectric elements disposed on a planar surface for radiating and receiving acoustic waves in a direction normal to that surface. By properly phasing these elements, the beam can be focused at a predetermined distance and scanned azimuthally. The elements being bilateral in function, two beams are generated in diametrically opposite directions. In general, to obtain good depth resolution, one of the beams must be absorbed and its energy dissipated in some form of an acoustic absorber.
An acoustic absorber should have an acoustic impedance that substantially matches the acoustic impedance of the piezoelectric elements, and typically comprises heavy metal particles such as tungsten sintered in a thermoplastic binder such as polyvinyl/chloride. Because the absorber (hereinafter also referred to as "backing") is electrically conductive, an intermediate layer of a non-conducting material must be inserted between the elements and the backing. The layers of material form a stack, each one of which must be acoustically matched to achieve maximum transfer of acoustic energy across the interfaces.
An acoustic transducer constructed according to the principles of the present invention comprises a tungsten-vinyl backing to absorb the unwanted acoustic energy, an electroplated alumina substrate of proper acoustic impedance, an alumina housing to support the acoustic stack and to provide structure for electrically connecting the transducer array elements to the system signal processing electronics, an array of PZT elements, a grounding foil, and an acoustic lens.